Dissolve the yeast in 3 tbsp of warm water. Add 3.5 oz flour and mix the ingredients together to form a loaf of dough. Transfer dough to a floured bowl and make a little cross on top with the tip of a knife. Cover and let rise for 20 minutes in a warm place. Allow the dough to double in volume. Form a well with the rest of the flour on a work surface. Sprinkle with salt. Add 3 tbsp of oil and dough ball to the center. Work together the ingredients, adding about 6 tbsp of warm water. Continue kneading until the dough is smooth and doesn't stick to your hands. For a loaf with the dough and make an cross on top. Let rise for an hour in a floured bowl. Grease the baking sheet with oil and stretch out the dough to cover the entire sheet. Let rise for another half and hour. Peel and thinly slice the onion. Blanch in boiling water for 2 minutes. Drain well and cover the dough with the onions. Sprinkle with salt and pepper and drizzle with a little oil. Bake in a 500 °F oven for 10 to 15 minutes.